Crumbling internal block work

[shockfire]

Hi all,

We have a cavity wall, where the outside is clay bricks and the inside is concrete blocks.

However, in some places (seemingly randomly throughout all 3 outside walls), the concrete blocks have "dents" in them. When placing a finger in a "dent", the block begins to crumble and the dent gets bigger. There is no sign of rising damp, and nothing "feels" wet.

Does anyone know what could be causing this problem? Searched all over but cannot find any information.

Thanks for your help :),
Shockfire.

[stoneyboy]

shockfire,
I assume you are refering to aerated concrete blocks. You may have a bad batch where large air pockets have been formed in the block - you will end up with a hollow cavity.
Alternatively the block layer has used a hammer to lay the blocks and damaged the surface.
end